System and method for dynamically regulating a step down power supply

ABSTRACT

A low gain feedback compensation circuit is provided on an integrated circuit. The feedback compensation circuit is coupled to a step down power supply on the integrated circuit. The step down power supply is operable to receive an input voltage and to generate an output voltage based on the input voltage. The feedback compensation circuit includes a line regulation circuit. The line regulation circuit is operable to receive the input voltage and a reference voltage. The line regulation circuit is also operable to generate an offset voltage based on the input voltage and the reference voltage.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates generally to the field of semiconductordevices and more particularly to a system and method for dynamicallyregulating a step down power supply.

BACKGROUND OF THE INVENTION

[0002] Modern electronic equipment such as televisions, telephones,radios and computers are generally constructed of solid state devices.Integrated circuits are preferred in electronic equipment because theyare extremely small and relatively inexpensive. Additionally, integratedcircuits are very reliable because they have no moving parts but arebased on the movement of charge carriers.

[0003] Integrated circuits may include transistors, capacitors,resistors and other semiconductor devices. Typically, such devices arefabricated on a substrate and interconnected to form power supplies,memory arrays, logic structures, timers and other components of anintegrated circuit. One type of power supply is a step down power supplywhich is operable to receive an input voltage and step down the inputvoltage to a specified output voltage.

[0004] Conventional step down power supplies include high gain, such as60 to 80 dB, feedback compensation. High gain feedback compensationgenerally provides good line regulation and initial accuracy for thestep down power supply. However, high gain feedback compensationtypically uses up to seven feedback components, including resistors andcapacitors. The capacitors may be too large for integration into thestep down power supply. Thus, typical step down power supplies usinghigh gain feedback compensation have the feedback components external tothe step down integrated circuit. In addition, the transient responseassociated with high gain feedback compensation is limited due to thedominant pole in the feedback network.

[0005] Low gain, such as less than 40 dB, feedback compensation may beused to reduce the number of feedback components, which may also allowintegration into the step down integrated circuit. Also, the transientresponse is not limited by a pole for a typical low gain feedbackcompensation. However, poor line regulation generally results from lowgain feedback compensation for a step down power supply. Furthermore,typical step down power supplies with low gain feedback compensationhave initial accuracy errors and burden the designer with solving thisproblem by having the customer select the resistor values to correct theerrors.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, a system and method fordynamically regulating a step down power supply are provided thatsubstantially eliminate or reduce disadvantages and problems associatedwith previously developed systems and methods. In a particularembodiment, low gain feedback compensation is provided in a step downpower supply with initial accuracy errors minimized and with relativelygood line regulation, which is accomplished by introducing an offsetvoltage.

[0007] According to one embodiment of the present invention, a low gainfeedback compensation circuit is provided on an integrated circuit. Thefeedback compensation circuit is coupled to a step down power supply onthe integrated circuit. The step down power supply is operable toreceive an input voltage and to generate an output voltage based on theinput voltage. The feedback compensation circuit includes a lineregulation circuit. The line regulation circuit is operable to receivethe input voltage and a reference voltage. The line regulation circuitis also operable to generate an offset voltage based on the inputvoltage and the reference voltage.

[0008] According to another embodiment of the present invention, amethod for dynamically regulating an output voltage for a step downpower supply is provided. The method includes providing a referencevoltage to an error amplifier for a low gain feedback compensationcircuit. The feedback compensation circuit includes a line regulationcircuit. The reference voltage is received at the line regulationcircuit. A first input voltage is received at the line regulationcircuit. A first offset voltage is provided to the error amplifier basedon the first input voltage and the reference voltage. A second inputvoltage is received at the line regulation circuit. The second inputvoltage is different from the first input voltage. A second offsetvoltage is provided to the error amplifier based on the second inputvoltage and the reference voltage.

[0009] Technical advantages of one or more embodiments of the presentinvention include providing an improved system for dynamicallyregulating a step down power supply. In a particular embodiment, acurrent source provides an offset voltage that is a function of theinput voltage and the desired output voltage. As a result, the lineregulation is improved and initial accuracy errors are minimized.

[0010] Other technical advantages of one or more embodiments of thepresent invention include integrating a feedback compensation circuitthat includes a line regulation circuit into a step down integratedcircuit. Accordingly, available die area is increased. In addition, thenumber of components and the output voltage error due to line voltagechanges are minimized.

[0011] Technical advantages of one or more embodiments of the presentinvention also include providing a feedback compensation circuit thathas only resistors. As a result, capacitors for the feedbackcompensation circuit do not need to be integrated into the step downintegrated circuit.

[0012] Other technical advantages will be readily apparent to oneskilled in the art from the following figures, descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of the present invention andits advantages is now made to the following description taken inconjunction with the accompanying drawings, wherein like numeralsrepresent like parts, in which:

[0014]FIG. 1 is a block diagram illustrating a step down integratedcircuit in accordance with one embodiment of the present invention;

[0015]FIG. 2A is a schematic diagram illustrating the feedbackcompensation circuit of FIG. 1 in accordance with one embodiment of thepresent invention;

[0016]FIG. 2B is a schematic diagram illustrating the feedbackcompensation circuit of FIG. 1 in accordance with an alternativeembodiment of the present invention;

[0017]FIG. 3 is a graph illustrating a duty cycle for the pulse widthmodulation comparator of FIGS. 2A or 2B in accordance with oneembodiment of the present invention;

[0018]FIG. 4A is a schematic diagram illustrating the feedbackcompensation circuit and the line regulation circuit of FIG. 1 inaccordance with one embodiment of the present invention;

[0019]FIG. 4B is a flow diagram illustrating a method for configuringthe line regulation circuit of FIG. 1 to dynamically regulate the stepdown power supply of FIG. 1 in accordance with one embodiment of thepresent invention;

[0020]FIG. 4C is a flow diagram illustrating a method for dynamicallyregulating the step down power supply of FIG. 1 in accordance with oneembodiment of the present invention; and

[0021]FIG. 5 is a schematic diagram illustrating details of the stepdown integrated circuit of FIG. 1 in accordance with one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022]FIG. 1 is a block diagram illustrating a step down integratedcircuit 10 in accordance with one embodiment of the present invention.The integrated circuit 10 may be used as a power supply that is operableto provide a relatively constant voltage to applications such as digitalsignal processors, field-programmable gate arrays, application-specificintegrated circuits, microprocessors and other suitable applications.

[0023] The integrated circuit 10 comprises a step down power supply 12and a feedback compensation circuit 14 formed on an integrated circuit.The step down power supply 12 is operable to step down an input voltage18 to a lower output voltage 20. For example, the step down power supply12 may receive an input voltage 18 of approximately 5.0 volts and maygenerate an output voltage 20 of approximately 3.3 volts. It will beunderstood, however, that any suitable input voltages 18 may be receivedand output voltages 20 may be generated without departing from the scopeof the present invention.

[0024] The feedback compensation circuit 14 is operable to providefeedback from the output voltage 20 to the step down power supply 12. Inaddition, the feedback compensation circuit 14 comprises a lineregulation circuit 22 that is operable to regulate the output voltage 20based on the input voltage 18.

[0025] The feedback compensation circuit 14 comprises a low gainfeedback compensation circuit. As used herein, “low gain” means a gainof less than approximately 40 dB. According to one embodiment, thecharacteristics of an output filter (not shown in FIG. 1) that includesan inductor and a capacitor may be used to stabilize the step downintegrated circuit 10.

[0026] In operation, the step down power supply 12 receives the inputvoltage 18 and generates an output voltage 20 based on the input voltage18. The level of the output voltage 20 may be a function of a duty cyclefor the step down power supply 12, which provides the input voltage 18for a specified period of time during each cycle and which provides aground voltage for the remainder of each cycle.

[0027] The feedback compensation circuit 14 receives both the inputvoltage 18 and the output voltage 20. Based on the input voltage 18, theline regulation circuit 22 determines an offset voltage to be applied inaddition to a reference voltage provided by the feedback compensationcircuit 14. The line regulation circuit 22 then generates the offsetvoltage within the feedback compensation circuit 14 such that an errorvoltage 24 provided to the step down power supply 12 results in theregulation of the output voltage 20 to the appropriate level.

[0028] In this way, the line regulation circuit 22 may generate anoffset voltage that dynamically changes based on the input voltage 18,resulting in the minimization of initial accuracy errors and lineregulation errors. In addition, the feedback compensation circuit 14including the line regulation circuit 22 may be integrated with the stepdown power supply 12 onto the step down integrated circuit 10, providingincreased die area for other components.

[0029]FIG. 2A is a schematic diagram illustrating the feedbackcompensation circuit 14 in accordance with one embodiment of the presentinvention. The feedback compensation circuit 14 comprises an erroramplifier 40, a reference voltage 44, a plurality of resistors 50, andthe line regulation circuit 22. It will be understood that additionalcomponents, such as capacitors, may be included in the feedbackcompensation circuit 14.

[0030] In accordance with the illustrated embodiment, the lineregulation circuit 22 comprises a current source. It will be understood,however, that the line regulation circuit 22 may be otherwise suitablyimplemented without departing from the scope of the present invention.

[0031] The reference voltage 44 is coupled to the non-inverting node ofthe error amplifier 40. An input resistor 50 a couples the outputvoltage 20 to the inverting node of the error amplifier 40. A feedbackresistor 50 b couples the output of the error amplifier 40, which is theerror voltage 24, to the inverting node of the error amplifier 40. Theline regulation circuit 22 couples the input voltage 18 to the invertingnode of the error amplifier 40.

[0032] In the illustrated embodiment, the error voltage 24 is coupled tothe non-inverting node of a pulse width modulation (PWM) comparator 64,which is part of the step down power supply 12. An oscillator 66, whichis also part of the step down power supply 12, is coupled to theinverting node of the PWM comparator 64. Thus, the error voltage 24 andthe oscillator 66, in conjunction with a duty cycle for the PWMcomparator 64, determine the output for the PWM comparator 64.

[0033] According to one embodiment, the oscillator 66 may have anoscillator frequency of approximately 270 to 700 kHz. In a particularembodiment, the oscillator frequency is approximately 350 kHz. Inanother particular embodiment, the oscillator frequency is approximately550 kHz. However, it will be understood that the oscillator frequencymay comprise any suitable frequency without departing from the scope ofthe present invention.

[0034] In accordance with one embodiment of the present invention, thefeedback compensation circuit 14 illustrated in FIG. 2A is operable toregulate a corresponding step down power supply 12 that is generating anoutput voltage 20 of less than approximately 1.8 volts. In a particularembodiment, the illustrated feedback compensation circuit 14 is operableto regulate a corresponding step down power supply 12 that is generatingan output voltage 20 of approximately 0.9, 1.2 or 1.5 volts.

[0035] The reference voltage 44 may be operable to provide to the erroramplifier 40 a reference voltage of approximately the same voltage asthe output voltage 20. In addition, the resistors 50 may comprise a 2 kΩinput resistor 50 a and a 40 kΩ feedback resistor 50 b. For thisembodiment, the feedback compensation circuit 14 may comprise a gain ofapproximately 26 dB. It will be understood, however, that any suitablevalues may be used for the resistors 50 and any suitable low gain may beprovided by the feedback compensation circuit 14 without departing fromthe scope of the present invention.

[0036] In operation, the line regulation circuit 22 receives the inputvoltage 18. Based on the input voltage 18, the line regulation circuit22 provides an offset voltage to the error amplifier 40 by generating aspecified current. Thus, if the input voltage 18 subsequently changes,the line regulation circuit 22 generates a different current, whichprovides a different offset voltage to the error amplifier 40. The newoffset voltage allows the same output voltage 20 to be generated by thestep down power supply 12 regardless of a change in the input voltage18.

[0037] For the illustrated embodiment, only two resistors 50 and nocapacitors are included in the feedback compensation circuit 14. In thisway, the feedback compensation circuit 14 may be integrated onto thestep down integrated circuit 10 relatively easily, while initialaccuracy errors and line regulation errors are minimized by the offsetvoltage provided through the line regulation circuit 22.

[0038]FIG. 2B is a schematic diagram illustrating the line regulationcircuit 14 in accordance with an alternative embodiment of the presentinvention. The line regulation circuit 14 comprises an error amplifier40, a reference voltage 44, a plurality of resistors 50, and the lineregulation circuit 22. It will be understood that additional components,such as capacitors, may be included in the feedback compensation circuit14.

[0039] In accordance with the illustrated embodiment, the lineregulation circuit 22 comprises a current source. It will be understood,however, that the line regulation circuit 22 may be otherwise suitablyimplemented without departing from the scope of the present invention.

[0040] The reference voltage 44 is coupled to the non-inverting node ofthe error amplifier 40. A first input resistor 50 c couples the outputvoltage 20 to the inverting node of the error amplifier 40. A feedbackresistor 50 d couples the output of the error amplifier 40, which is theerror voltage 24, to the inverting node of the error amplifier 40. Asecond input resistor 50 e couples ground 68 to the inverting node ofthe error amplifier 40. The line regulation circuit 22 couples the inputvoltage 18 to the inverting node of the error amplifier 40.

[0041] According to one embodiment, the ground 68 comprises a potentialof approximately 0.0 volts. However, it will be understood that theground 68 may comprise any suitable potential that is less thanpotential of the input voltage 18.

[0042] In the illustrated embodiment, the error voltage 24 is coupled tothe non-inverting node of a PWM comparator 64, which is part of the stepdown power supply 12. An oscillator 66, which is also part of the stepdown power supply 12, is coupled to the inverting node of the PWMcomparator 64. Thus, the error voltage 24 and the oscillator 66, inconjunction with a duty cycle for the PWM comparator 64, determine theoutput for the PWM comparator 64.

[0043] According to one embodiment, the oscillator 66 may have anoscillator frequency of approximately 270 to 700 kHz. In a particularembodiment, the oscillator frequency is approximately 350 kHz. Inanother particular embodiment, the oscillator frequency is approximately550 kHz. However, it will be understood that the oscillator frequencymay comprise any suitable frequency without departing from the scope ofthe present invention.

[0044] In accordance with one embodiment of the present invention, thefeedback compensation circuit 14 illustrated in FIG. 2A is operable toregulate a corresponding step down power supply 12 that is generating anoutput voltage 20 of more than approximately 1.5 volts. In a particularembodiment, the illustrated feedback compensation circuit 14 is operableto regulate a corresponding step down power supply 12 that is generatingan output voltage 20 of approximately 1.8, 2.5 or 3.3 volts.

[0045] The reference voltage 44 may be operable to provide to the erroramplifier 40 a reference voltage of approximately 50% of the outputvoltage 20. For this embodiment, the input resistors 50 c and 50 e maycomprise approximately the same resistance. In one embodiment, theresistors 50 may comprise a 2 kΩ first input resistor 50 c, a 2 kΩsecond input resistor 50 e, and a 40 kΩ feedback resistor 50 d. For thisembodiment, the feedback compensation circuit 14 may comprise a gain ofapproximately 26 dB. It will be understood, however, that any suitablevalues may be used for the resistors 50 and any suitable low gain may beprovided by the feedback compensation circuit 14 without departing fromthe scope of the present invention.

[0046] In operation, the line regulation circuit 22 receives the inputvoltage 18. Based on the input voltage 18, the line regulation circuit22 provides an offset voltage to the error amplifier 40 by generating aspecified current. Thus, if the input voltage 18 subsequently changes,the line regulation circuit 22 generates a different current, whichprovides a different offset voltage to the error amplifier 40. The newoffset voltage allows the same output voltage 20 to be generated by thestep down power supply 12 regardless of a change in the input voltage18.

[0047] For the illustrated embodiment, only three resistors 50 and nocapacitors are included in the feedback compensation circuit 14. In thisway, the feedback compensation circuit 14 may be integrated onto thestep down integrated circuit 10 relatively easily, while initialaccuracy errors and line regulation errors are minimized by the offsetvoltage provided through the line regulation circuit 22.

[0048] In an alternative embodiment, the reference voltage 44 may bevaried based on the input voltage 18 instead of using the lineregulation circuit 22 to provide an offset voltage.

[0049]FIG. 3 is a graph 70 illustrating a duty cycle 72 for the PWMcomparator 64 in accordance with one embodiment of the presentinvention. The graph 70 illustrates voltage provided by the oscillator66 to the PWM comparator 64 as a function of time. The graph 70 alsoillustrates the error voltage 24 provided by the feedback compensationcircuit 14, as described in more detail above in connection with FIGS.1-2.

[0050] The voltage from the oscillator 66 varies cyclically from a lowvoltage 74 to a high voltage 76. As shown in FIG. 3 the PWM comparator64 is “on” until the voltage from the oscillator 66 reaches the errorvoltage 24 and “off” until the voltage from the oscillator 66 returns tothe low voltage 74. Each duty cycle 72 for the PWM comparator 64 is madeup of an on time 82 and an off time 84. While the PWM comparator 64 is“on,” the PWM comparator 64 outputs the error voltage 24, and while thePWM comparator 64 is “off,” the PWM comparator 64 outputs no signal.

[0051] The low voltage 74 and the high voltage 76 may be determinedbased on the characteristics of the PWM comparator 64. According to oneembodiment, the low voltage 74 is approximately 0.75 volts and the highvoltage 76 is approximately 1.75 volts. In addition, the differencebetween the low and high voltages 74 and 76 may be based on thecharacteristics of the step down power supply 12. According to oneembodiment, the difference may be approximately 0.5, 1.0 or 2.0 volts.It will be understood, however, that the low and high voltages 74 and 76and the difference between them may be any suitable values withoutdeparting from the scope of the present invention.

[0052] Based on the feedback compensation circuits 14 illustrated inFIGS. 2A and 2B and based on the duty cycle 72 for the PWM comparator 64illustrated in FIG. 3, the following equations for the step downintegrated circuit 10 may be generated:

(V _(ref) −V _(out))*A _(v) =V _(err)  (eqn. 1)

V _(err)=(V _(H) −V _(L))*(T _(on) /T)+V _(L)  (eqn. 2)

V _(err)=(V _(H) −V _(L))*D+V _(L)  (eqn. 3)

V _(err)=(V _(H) −V _(L))*(V _(out) /V _(in))+V _(L)  (eqn. 4)

V _(out)=(A _(v) * V _(ref) −V _(L))/[A _(v)+(V _(H) −V _(L))/V_(in)]  (eqn. 5),

[0053] where V_(ref) is the reference voltage 44, V_(out) is the outputvoltage 20, A_(v) is the gain of the error amplifier 40, V_(err) is theerror voltage 24, V_(H) is the high voltage 76 from the oscillator 66,V_(L) is the low voltage 74 from the oscillator 66, T_(on) is the ontime 82 for the PWM comparator 64, T is the time corresponding to oneduty cycle 72 for the PWM comparator 64 (or the on time 82 added to theoff time 84 for one duty cycle 72), D is the duty cycle 72 for the PWMcomparator 64, and V_(in) is the input voltage 18.

[0054] Thus, Equation 5 provides the output voltage error which resultsfrom the low gain feedback on the error amplifier 40. To determine anoffset voltage to compensate for this output voltage error, Equation 5may be solved for V_(ref) at the desired input voltage 18 and at thedesired output voltage 20. Then another equation may be generated fromthe differences in the actual reference voltage 44 and the referencevoltage which should be applied to the error amplifier 40 to result inthe appropriate output voltage 20, with the equation in the form of:

V _(off) =A*V _(in) +B  (eqn. 6)

[0055] Using the form of Equation 6, offset equations may be solved fora plurality of output voltages 20 in the form of the followingequations:

V _(off) =A ₁ *V _(in) +B ₁  (eqn. 7)

V _(off) =A ₂ *V _(in) +B ₂  (eqn. 8)

[0056] The A coefficients vary with respect to the output voltage 20 andmay be represented by another linear equation in the following form:

A=C*V _(out) +D  (eqn. 9)

[0057] Thus, substituting Equation 9 into Equation 6 yields a singleequation that may be used to minimize the offset error over a range ofinput voltages 18 for a corresponding output voltage 20:

V _(off)=(C*V _(out) +D)*V _(in) +B  (eqn. 10)

[0058] According to one embodiment, as V_(in) changes, the offsetvoltage changes in accordance with Equation 10. For the feedbackcompensation circuit 14 illustrated in FIG. 2A, the line regulationcircuit 22 generates an offset current to provide the offset voltagedetermined by Equation 10. This offset current is determined as follows:

I _(off) =[V _(off)*(1+R _(f) /R _(i1))]/R _(f)  (eqn. 11),

[0059] where I_(off) is the offset current, R_(f) is the resistance ofthe feedback resistor 50 b, and R_(i1) is the resistance of the inputresistor 50 a.

[0060] For the feedback compensation circuit 14 illustrated in FIG. 2B,the line regulation circuit 22 also generates an offset current toprovide the offset voltage determined by Equation 10. However, theoffset current for this embodiment is determined as follows:

I _(off) =V _(off)*(1/R _(f)+1/R _(i1)+1/R _(i2))  (eqn. 12),

[0061] where R_(f) is the resistance of the feedback resistor 50 d,R_(i1) is the resistance of the first input resistor 50 c, and R_(i2) isthe resistance of the second input resistor 50 e.

[0062]FIG. 4A is a schematic diagram illustrating the feedbackcompensation circuit 14 and the line regulation circuit 22 in accordancewith one embodiment of the present invention. The line regulationcircuit 22 comprises an offset voltage function 90. The offset voltagefunction 90 is operable to receive the input voltage 18 and thereference voltage 44 and is configured to generate an offset voltagebased on the input voltage 18 and the reference voltage 44.

[0063] According to one embodiment, the offset voltage function 90 isconfigured in accordance with the method of FIG. 4B. However, it will beunderstood that the offset voltage function 90 may be otherwise suitablyconfigured without departing from the scope of the present invention.Also, according to one embodiment, the offset voltage function 90 isoperable to generate the offset voltage in accordance with the method ofFIG. 4C. However, it will be understood that the offset voltage function90 may otherwise suitably generate the offset voltage without departingfrom the scope of the present invention.

[0064] The feedback compensation circuit 14 comprises an adder 92 thatis operable to receive the offset voltage from the offset voltagefunction 90 and to receive the output voltage 20. Based on the offsetvoltage from the offset voltage function 90 and the output voltage 20,the adder 92 generates an output for the feedback compensation circuit14, as illustrated.

[0065]FIG. 4B is a flow diagram illustrating a method for configuringthe line regulation circuit 22 to dynamically regulate the step downpower supply 12 in accordance with one embodiment of the presentinvention. The method begins at step 100 where an output voltage erroris determined for the line regulation circuit 22. According to oneembodiment, the output voltage error is determined based on Equation 5,above.

[0066] At step 102, an equation for calculating an offset voltage isdetermined based on the reference voltage and the output voltage errordetermined in step 100. According to one embodiment, the offset voltageequation comprises Equation 10, above.

[0067] In this way, an offset voltage equation may be determined for theline regulation circuit 22. The line regulation circuit 22 may then beconfigured in accordance with the offset voltage equation such that theinput voltage 18 received by the line regulation circuit 22 results inthe appropriate offset voltage being generated by the line regulationcircuit 22 for the feedback compensation circuit 14.

[0068]FIG. 4C is a flow diagram illustrating a method for dynamicallyregulating the step down power supply 12 in accordance with oneembodiment of the present invention. The method begins at step 104 wherethe line regulation circuit 22 determines the offset voltage based onthe input voltage 18 received at the line regulation circuit 22 and anoffset voltage equation. According to one embodiment, the offset voltageequation is determined in accordance with step 102 of FIG. 4B. Thus, theline regulation circuit 22 may determine the offset voltage based on theconfiguration of the line regulation circuit 22, which is based on theoffset voltage equation, in conjunction with the input voltage 18.

[0069] At step 106, the line regulation circuit 22 provides an offsetcurrent to the feedback compensation circuit 14 based on the offsetvoltage determined in step 104. According to the embodiment illustratedin FIG. 2A, the offset current may be determined based on Equation 11,above. According to the embodiment illustrated in FIG. 2B, the offsetcurrent may be determined based on Equation 12, above. It will beunderstood that the line regulation circuit 22 may provide the offsetcurrent based on the configuration of the line regulation circuit 22,which may be accomplished in accordance with the method of FIG. 4B.

[0070] At decisional step 108, the line regulation circuit 22 determineswhether or not the input voltage 18 has changed. If the input voltage 18has not changed, the method follows the No branch from decisional step108 and returns to the same step to monitor the input voltage 18 for achange.

[0071] If the input voltage 18 has changed, the method follows the Yesbranch from decisional step 108 and returns to step 104 where a newoffset voltage is determined based on the new input voltage. The methodthen continues to step 106 where the line regulation circuit 22 providesa new offset current to the feedback compensation circuit 14 based onthe new offset voltage determined in step 104 before monitoring theinput voltage 18 for another change. In this way, the line regulationcircuit 22 may continuously monitor the input voltage 18 in order todynamically generate an appropriate offset voltage for the feedbackcompensation circuit 14.

[0072]FIG. 5 is a schematic diagram illustrating details of the stepdown integrated circuit 10 in accordance with one embodiment of thepresent invention. For this embodiment, the input voltage 18 may varyfrom approximately 2.7 to 5.0 volts, the output voltage 20 may vary fromapproximately 1.8 to 3.3 volts, the reference voltage 44 isapproximately 0.891 volts, the input resistor 50 a comprisesapproximately 2 kΩ, and the feedback resistor 50 b comprisesapproximately 40 kΩ. However, it will be understood that the step downintegrated circuit 10 may be otherwise suitably implemented withoutdeparting from the scope of the present invention.

[0073] Although the present invention has been described with severalembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present invention encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A low gain feedback compensation circuit on anintegrated circuit, the feedback compensation circuit coupled to a stepdown power supply on the integrated circuit, the step down power supplyoperable to receive an input voltage and to generate an output voltagebased on the input voltage, the feedback compensation circuit comprisinga line regulation circuit operable to receive the input voltage and areference voltage and operable to generate an offset voltage based onthe input voltage and the reference voltage.
 2. The circuit of claim 1,further comprising: an error amplifier coupled to the line regulationcircuit; the reference voltage coupled to the error amplifier; and theline regulation circuit further operable to provide the offset voltageto the error amplifier.
 3. The circuit of claim 2, the error amplifieroperable to provide a gain of approximately 26 dB.
 4. The circuit ofclaim 1, further comprising a single feedback resistor and a singleinput resistor.
 5. The circuit of claim 1, further comprising a singlefeedback resistor and two input resistors.
 6. The circuit of claim 1,the line regulation circuit comprising a current source.
 7. A system fordynamically regulating a step down power supply, comprising: a step downpower supply on an integrated circuit, the step down power supplyoperable to receive an input voltage and to generate an output voltagebased on the input voltage; and a low gain feedback compensation circuiton the integrated circuit, the feedback compensation circuit coupled tothe step down power supply and operable to receive the input voltage,the feedback compensation circuit comprising a line regulation circuitoperable to receive the input voltage and a reference voltage andoperable to generate an offset voltage based on the input voltage andthe reference voltage.
 8. The system of claim 7, the feedbackcompensation circuit further comprising an error amplifier coupled tothe line regulation circuit, the reference voltage coupled to the erroramplifier, and the line regulation circuit further operable to providethe offset voltage to the error amplifier.
 9. The system of claim 8, theerror amplifier operable to provide a gain of approximately 26 dB. 10.The system of claim 7, the feedback compensation circuit furthercomprising a single feedback resistor and a single input resistor. 11.The system of claim 7, the feedback compensation circuit furthercomprising a single feedback resistor and two input resistors.
 12. Thesystem of claim 7, the line regulation circuit comprising a currentsource.
 13. A method for dynamically regulating an output voltage for astep down power supply, comprising: providing a reference voltage to anerror amplifier for a low gain feedback compensation circuit, thefeedback compensation circuit comprising a line regulation circuit;receiving the reference voltage at the line regulation circuit;receiving a first input voltage at the line regulation circuit;providing a first offset voltage to the error amplifier based on thefirst input voltage and the reference voltage; receiving a second inputvoltage at the line regulation circuit, the second input voltagedifferent from the first input voltage; and providing a second offsetvoltage to the error amplifier based on the second input voltage and thereference voltage.
 14. The method of claim 13, the line regulationcircuit comprising a current source.
 15. The method of claim 13, furthercomprising: determining an output voltage error for the line regulationcircuit; and determining an offset voltage equation based on thereference voltage and the output voltage error.
 16. The method of claim15, further comprising: determining the first offset voltage based onthe first input voltage, the reference voltage, and the offset voltageequation; and determining the second offset voltage based on the secondinput voltage, the reference voltage, and the offset voltage equation.17. The method of claim 13, further comprising providing a gain for thefeedback compensation circuit of approximately 26 dB with the erroramplifier.
 18. The method of claim 13, the feedback compensation circuitfurther comprising a single feedback resistor and a single inputresistor.
 19. The method of claim 13, the feedback compensation circuitfurther comprising a single feedback resistor and two input resistors.20. The method of claim 15, the reference voltage approximately the sameas the output voltage.